Golf Balls Including A Crosslinked Thermoplastic Polyurethane Cover Layer Having Improved Scuff Resistance

ABSTRACT

This disclosure relates to golf balls having a cover layer made from a crosslinked thermoplastic polyurethane elastomer. The crosslinked thermoplastic polyurethane elastomer includes crosslinks located in the hard segments, where the crosslinks being the reaction product of unsaturated bonds located in the hard segments catalyzed by a free radical initiator. The crosslinks may be formed from an unsaturated diol as a chain extender. The unsaturated diol may be trimethylolpropane monoallylether (TMPME). The cover layer may have certain properties, such as a desirable flexural modulus value and a desirable Shore D hardness value, that further contribute to the golf ball having a high degree of scuff resistance.

STATEMENT OF RELATED APPLICATIONS

This application is a continuation-in-part application of co-pendingapplication Ser. No. 12/827,360, filed Jun. 30, 2010 the entirety ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to golf balls and their manufacture, andin particular to golf balls having thermoplastic polyurethane covers.

2. Description of Related Art

Golf ball covers are generally divided into two types: thermoplasticcovers and thermoset covers. Thermoplastic polymer materials may bereversibly melted, and so may be used in a variety of manufacturingtechniques such as compression molding that take advantage of thisproperty. On the other hand, thermoset polymer materials are generallyformed by mixing two or more components to form a cured polymer materialthat cannot be re-melted or re-worked. Each type of polymer materialpresent advantages and disadvantages when used to manufacture golfballs.

Thermoplastic materials for golf ball covers often include ionomerresin, highly neutralized acid polymer composition, polyamide resin,polyester resin, polyurethane resin, and mixtures thereof. Among these,ionomer resin and polyurethane resin are popular materials for golf ballcovers.

Ionomer resins, such as Surlyn® resins (commercially available from E.I. DuPont de Nemours and Company), have conventionally been used forgolf ball covers. For example, Dunlop Rubber Company obtained the firstpatent on the use of Surlyn® for the cover of a golf ball, U.S. Pat. No.3,454,280 issued Jul. 8, 1969. Since then, there have been a number ofdisclosures on the use of ionomer resins in the cover composition of agolf ball, for example, U.S. Pat. Nos. 3,819,768, 4,323,247, 4,526,375,4,884,814, and 4,911,451.

However, ionomer resin covered golf balls suffer from the problem thatthe cover surface may be scraped off by grooves on a clubface duringrepeated shots, particularly with irons. In other words, ionomer covershave poor scuff resistance. Also, ionomer covered balls usually haveinferior spin and feel properties as compared to balata rubber orpolyurethane covered balls. The use of softer ionomer resins for thecover will improve spin and feel to some extent, but will alsocompromise the resilience of the golf balls because such balls usuallyhave a lower coefficient of restitution (C.O.R.). Furthermore, the scuffresistance of such softer ionomer covers is often still notsatisfactory.

Thermoplastic polyurethane elastomers may also be used as the covermaterial, as described in (for example) U.S. Pat. Nos. 3,395,109,4,248,432 and 4,442,282. However, the thermoplastic polyurethaneelastomers disclosed therein do not satisfy all the requirements ofmoldability, hitting feel, control, resilience, and scuff resistanceupon iron shots.

On the other hand, thermoset polymer materials such as polyurethaneelastomers, polyamide elastomers, polyurea elastomers, diene-containingpolymer, crosslinked metallocene catalyzed polyolefin, and silicone, mayalso be used to manufacture golf balls. Among these materials, thermosetpolyurethane elastomers are popular.

U.S. Pat. Nos. 3,989,568, 4,123,061, 5,334,673, and 5,885,172, describemany attempts to use thermoset polyurethane elastomers as a substitutefor balata rubber and ionomer resins. Thermosetting polyurethaneelastomers are relatively inexpensive and offer good hitting feel andgood scuff resistance. Particularly, thermoset polyurethane elastomersmay present improvements in the scuff resistance as compared to softenedionomer resin blends. However, thermoset materials require complexmanufacturing processes to introduce the raw material and then effect acuring reaction, which causes the manufacturing process to be lessefficient.

Accordingly, for the foregoing reasons, there is a need to develop agolf ball cover material with good scuff resistance that can beefficiently manufactured. There is a need in the art for a system andmethod that addresses the shortcomings of the prior art discussed above.

SUMMARY OF THE INVENTION

In one aspect, this disclosure provides a golf ball comprising: a core,and a cover layer substantially surrounding the core; wherein the coverlayer comprises a crosslinked thermoplastic polyurethane elastomer; thecrosslinked thermoplastic polyurethane elastomer including hard segmentsand soft segments, the crosslinked thermoplastic polyurethane elastomerincluding crosslinks located in the hard segments, the crosslinks beingthe reaction product of unsaturated bonds located in the hard segmentscatalyzed by a free radical initiator; and wherein the cover layer has aflexural modulus of from about 200 psi to about 10,000 psi.

In a particular embodiment of the above golf ball, this disclosureprovides a golf ball comprising: a core, and a cover layer substantiallysurrounding the core; wherein the cover layer comprises a crosslinkedthermoplastic polyurethane elastomer; the crosslinked thermoplasticpolyurethane elastomer including hard segments and soft segments, thecrosslinked thermoplastic polyurethane elastomer including crosslinkslocated in the hard segments, the crosslinks being the reaction productof unsaturated bonds located in the hard segments catalyzed by a freeradical initiator; and wherein the crosslinked thermoplasticpolyurethane elastomer is the reaction product of an unsaturated diol offormula (1):

in which R¹ may be any substituted or unsubstituted alkyl, substitutedor unsubstituted aryl, substituted or unsubstituted alkyl-aryl group,substituted or unsubstituted ether group, substituted or unsubstitutedester group, any combination of the above groups, or H, and mayoptionally include an unsaturated bond in any main chain or side chainof any group; R² may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups, andR² includes an allyl group; and x and y are integers independentlyhaving any value from 1 to 10.

In another aspect, the present disclosure provides a golf ballcomprising: an inner core layer, an outer core layer substantiallysurrounding the inner core layer, an inner cover layer substantiallysurrounding the outer core layer, and an outer cover layer substantiallysurrounding the inner cover layer; wherein the outer cover layercomprises a crosslinked thermoplastic polyurethane elastomer havingcrosslinks located in hard segments, the crosslinks being the reactionproduct of unsaturated bonds located in the hard segments catalyzed by afree radical initiator; and the golf ball satisfies the followingrequirements: (1) the outer cover layer has a Shore D hardness on thegolf ball from about 40 to about 65; and (2) the outer cover layer has aflexural modulus of from about 200 psi to about 10,000 psi.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one of ordinary skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description and this summary, bewithin the scope of the invention, and be protected by the followingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereference numerals designate corresponding parts throughout thedifferent views.

FIG. 1 shows a representative golf ball in accordance with thisdisclosure, the golf ball being of a two-piece construction;

FIG. 2 shows a second representative golf ball, having an inner coverlayer and an outer cover layer;

FIG. 3 shows a third representative golf ball, having an inner core andan outer core; and

FIG. 4 shows a fourth representative golf ball, having an inner core, anouter core, an inner cover layer, and an outer cover layer.

DETAILED DESCRIPTION

Generally, this disclosure relates to golf balls having a cover layermanufactured from a crosslinked thermoplastic polyurethane, where thecrosslinks are formed in the hard segments. In particular embodiments anouter cover layer may be made from the crosslinked thermoplasticpolyurethane, where the outer cover layer may have a desirable flexuralmodulus value. As a result of these features, the outer cover layer'sscuff resistance may be greatly improved.

Except as otherwise discussed herein below, any golf ball discussedherein may generally be any type of golf ball known in the art. Namely,unless the present disclosure indicates to the contrary, a golf ball maygenerally be of any construction conventionally used for golf balls, andmay be made of any of the various materials known to be used in golfball manufacturing. Furthermore, it is understood that any featuredisclosed herein (including but not limited to various embodiments shownin the FIGS. and various chemical formulas or mixtures) may be combinedwith any other features disclosed here, as may be desired.

FIG. 1 shows a golf ball 100 in accordance with a first embodiment ofthe present disclosure. Golf ball 100 is a two piece golf ball.Specifically, golf ball 100 includes cover layer 110 substantiallysurrounding core 120. In golf ball 100, cover layer 110 may be made of acrosslinked thermoplastic polyurethane elastomer.

The crosslinked thermoplastic polyurethane elastomer may include hardsegments and soft segments, as thermoplastic polyurethanes are known toinclude. Thermoplastic polyurethanes are generally made up of (1) a longchain polyol, (2) a relatively short chain extender, and (3) adiisocyanate. Once reacted, the portions of the polymer chain made up ofthe chain extender and diisocyanate generally align themselves intosemi-crystalline structures through weak (i.e., non-covalent)association, such as through Van der Waals forces, dipole-dipoleinteractions or hydrogen bonding. These portions are commonly referredto as the hard segments, because the semi-crystalline structure isharder than the amorphous portions made up of the long chain polyol.

The crosslinked thermoplastic polyurethane may include crosslinkslocated specifically in the hard segments. These crosslinks may be thereaction product of unsaturated bonds located in the hard segments,catalyzed by a free radical initiator. These unsaturated bonds may beintroduced into the hard segments by the use of unsaturated diols aschain extenders. In particular embodiments, the crosslinks may be formedfrom diol chain extenders having an unsaturated side chain.

Generally, the crosslinked thermoplastic polyurethane may be derivedfrom reacting a mixture of:

-   (a) an organic isocyanate;-   (b) an unsaturated diol first chain extender;-   (c) optionally, a second chain extender having at least two reaction    sites with isocyanates and having a molecular weight of less than    about 450;-   (d) a long chain polyol having a molecular weight of between about    500 and about 4,000; and-   (e) a sufficient amount of free radical initiator, so as to be    capable of generating free radicals that induce crosslinking    structures in the hard segments by free radical initiation.

Each of the above listed reactants will be discussed in further detail,with the understanding that any particular embodiment of a specificreactant may be mixed and matched with any other specific embodiment ofanother reactant according to the general formulation above.Furthermore, any reactant may generally be used in combination withother reactants of the same type, such that any list herein includesmixtures thereof, unless otherwise specified.

The organic isocyanate may include any of the known aromatic, aliphatic,and cycloaliphatic di- or polyisocyanates. Examples of suitableisocyanates include: 2,2′-, 2,4′- (and particularly) 4,4-diphenylmethanediisocyanate, and isomeric mixtures thereof (“MDI”); polyphenylenepolymethylene polyisocyanates (poly-MDI, PMDI); 2,4- and 2,6-toluenediisocyanates, and isomeric mixtures thereof such as an 80:20 mixture ofthe 2,4- and 2,6-isomers (“TDI”); isophorone diisocyanate;1,4-diisocyanatobutane; 1,5-diisocyanatopentane; 1,6-diisocyanatohexane;1,4-cyclohexane diisocyanate; cycloaliphatic analogs of PMDI; and thelike.

The unsaturated diol first chain extender is discussed substantiallybelow.

Suitable optional second chain extenders may include the common diols,such as ethylene glycol, diethylene glycol, triethylene glycol,propylene glycol, dipropylene glycol, tripropylene glycol,1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol,neopentyl glycol, dihydroxyethoxy hydroquinone,1,4-cyclo-hexanedimethanol, 1,4-dihydroxycyclohexane, and the like.Minor amounts of crosslinking agents such as glycerine,trimethylolpropane, diethanolamine, and triethanolamine may be used inconjunction with the diol chain extenders.

In addition to the common diol chain extenders, diamines and aminoalcohols may also be used as the optional second chain extender.Examples of suitable diamines include aliphatic, cycloaliphatic oraromatic diamines. In particular, a diamine chain extender may beethylene diamine, hexamethylene diamine, 1,4-cyclohexyene diamine,benzidine, toluene diamine, diaminodiphenyl methane, the isomers ofphenylene diamine or hydrazine. Aromatic amines may also be used, suchas MOCA (4,4′-methylene-bis-o-chloroaniline), M-CDEA(4,4′-methylenebis(3-chloro-2-6-diethyl-aniline)). Examples of suitableamino alcohols are ethanol amine, N-methylethanolamine,N-butylethanolamine, N-oleyethanolamine, N-cyclohexylisopropanolamine,and the like. Mixtures of various types of chain extenders may also beused to form the crosslinked thermoplastic polyurethane.

The long chain polyol (“the polyol”) may generally be a polyester polyolor a polyether polyol. Accordingly, the crosslinked thermoplasticpolyurethane may be either general type of polyurethane: a polyetherbased polyurethane elastomer or a polyester based polyurethaneelastomer, or mixtures thereof.

The long chain polyol may be a polyhydroxy compound having a molecularweight between 500 and 4,000. Suitable long chain polyols may generallyinclude linear polyesters, polyethers, polycarbonates, polylactones(e.g., ε-caprolactone), and mixtures thereof. In addition to polyolshaving hydroxyl terminal groups, the polyol may include carboxyl, aminoor mercapto terminal groups.

Polyester polyols are produced by the reaction of dicarboxylic acids anddiols or esterifiable derivative thereof. Examples of suitabledicarboxylic acids include succinic acid, glutaric acid, adipic acid,suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid,maleic acid, fumaric acid, phthalic acid, isophthalic acid, andterephthalic acid. Examples of suitable diols include ethanediol,diethylene glycol, 1,2- and 1,3-propanediol, dipropylene glycol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol,glycerine and trimethylolpropanes, tripropylene glycol, tetraethyleneglycol, tetrapropylene glycol, tetramethylene glycol,1,4-cyclohexane-dimethanol, and the like. Both of the dicarboxylic acidsand diols can be used individually or in mixtures to make specificpolyesters in the practice applications.

Polyether polyols are prepared by the ring-opening additionpolymerization of an alkylene oxide with an initiator of a polyhydricalcohol. Examples of suitable polyether polyols are polypropylene glycol(PPG), polyethylene glycol (PEG), polytetramethylene ether glycol(PTMEG). Block copolymers such as combinations of polyoxypropylene andpolyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethyleneglycols, poly-1,4-tetramethylene and polyoxyethylene glycols are alsotypical in the present invention.

Polycarbonate polyols are made through a condensation reaction of diolswith phosgene, chloroformic acid ester, dialkyl carbonate or diallylcarbonate. Examples of diols in the suitable polycarbonate polyols ofthe crosslinked thermoplastic polyurethane elastomers are ethanediol,diethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol,neopentylglycol, and 1,5-pentanediol.

The crosslinked thermoplastic polyurethane elastomer may comprise asufficient amount of free radical initiator so as to be capable ofinducing crosslinking structures in the hard segments by free radicalinitiation. The free radical initiator may generate free radicalsthrough thermal cleavage or UV radiation. When the half-life of the freeradical initiator and its operation temperature are considered in themanufacturing process, the weight ratio of initiators to unsaturateddiols may be from 0.1:100 to 100:100. In particular embodiments, theweight ratio of free radical initiator to unsaturated diols may be about5:100.

A variety of known free radical initiators may be used as the radicalsource in order to make the present polyurethane elastomer having acrosslinking structure. Suitable radical initiators may includeperoxides, sulfurs, and sulfides, and peroxides may be particularlysuitable in some embodiments. The peroxides may be aliphatic peroxides,aromatic peroxides, or mixtures thereof. Peroxides such asdiacetylperoxide, di-tert-butyperoxide, dicumylperoxide,dibenzoylperoxide, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane,2,5-dimethyl-2,5-di(butylperoxy)-3-hexyne,2,5-bis-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxyl)valerate,1,4-bis-(t-butylperoxyisopropyl)-benzene, t-butyl peroxybenzoate,1,1-bis-(t-butylperoxy)-3,3,5 tri-methylcyclohexane, anddi(2,4-dichloro-benzoyl) peroxide may be used as the free radicalinitiator in some embodiments.

The unsaturated diol first chain extender may generally be any diolhaving at least one terminal pendant unsaturated bond. Generally, as isknown in the art of polyurethane chemistry, a diol is used as a chainextender in thermoplastic polyurethane by reacting each of the twohydroxyl groups with the isocyanate. Here, at least one terminal pendantunsaturated bond may then be used to create crosslinks between thepolyurethane backbones. As is generally known, an unsaturated bond maybe a double bond between two carbon atoms (as in an alkene) or a triplebond (as in an alkyne)

In particular embodiments, the unsaturated diol may have two primaryalcohol groups. The presence of two primary alcohol groups may result infavorable reaction kinetics, such that the crosslinked thermoplasticpolyurethane may be formed in an easily controlled “one step” continuousprocess.

An unsaturated side chain present on the diol may generally be anyalkyl, aryl, or alkyl-aryl group, ether group, or ester group includingat least one terminal vinyl group. In particular embodiments, theunsaturated side chain may include an allyl group. The unsaturated dioland its side chain may be represented by formula (1) shown below:

in which R¹ may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups, or H,and may optionally include an unsaturated bond in any main chain or sidechain of any group; R² may be any suitable substituted or unsubstitutedalkyl, substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups, andR² includes an allyl group; and x and y are integers independentlyhaving any value from 1 to 10.

The above mentioned chemical groups may have their conventionaldefinitions as is generally known in the art of chemistry. Specifically,an unsubstituted alkyl group includes any chemical group comprising onlycarbon and hydrogen linked by single bonds. A substituted alkyl groupmay include atoms other than carbon and hydrogen in a side chainportion, such as a halogen group, an inorganic group, or other wellknown functional groups. In some embodiments, a substituted orunsubstituted alkyl group may include from 1 to about 100 carbon atomsin the alkyl chain. In other embodiments, a substituted or unsubstitutedalkyl group may have from 1 to 10 carbon atoms in the alkyl chain. Analkyl group, or any portion thereof, or alkyl substituent, may be astraight chain or branched.

As is further known in the art of chemistry, an aryl group is defined asany group that includes an aromatic benzene ring. Furthermore, analkyl-aryl group includes at least one aromatic benzene ring in additionto at least one alkyl carbon. An ether group includes at least oneoxygen atom bonded to two carbon atoms. An ester group includes at leastone carbon atom that is double bonded to a first oxygen atom and singlebonded to a second oxygen atom.

In some embodiments substituted groups, such as a substituted alkylgroup or a substitute aryl group, may be substituted with another of thesame group. For example, an alkyl may be substituted with another alkylto create a branched alkyl group. In other embodiments substitutedgroups may be substituted with a different group, for example an alkylmay be substituted with an ether group, or an ether group may besubstituted with an alkyl group. A person having ordinary skill in theart of chemistry may also synthesize suitable combinations of thesegroups, as may be desired.

In specific embodiments, the unsaturated diol may include an allyl ethergroup as the side chain. For example, the unsaturated diol may berepresented by formula (2) shown below:

in which R is a substituted or unsubstituted alkyl group, and x and yare integers independently having values of 1 to 4. In particularembodiments, x and y may both have values of 1, 2, 3 or 4. In otherembodiments, x and y may each have different values from 1 to 4.

In one particular embodiment, the unsaturated diol may betrimethylolpropane monoallylether (“TMPME”). TMPME may also be named“trimethylol propane monoallyl ether”, “trimethylol propanemonoallylether”, or “trimethylolpropane monoallyl ether.” TMPME has CASno. 682-11-1. TMPME may also be referred to as 1,3-Propanediol,2-ethyl-2-[(2-propen-1-yloxy)methyl] or as2-allyloxymethyl-2-ethyl-1,3-propanediol. TMPME is commerciallyavailable from Perstorp Specialty Chemicals AB.

Other suitable compounds that may be used as the unsaturated diol offormula (1) or formula (2) may include: 1,3-Propanediol,2-(2-propen-1-yl)-2-[(2-propen-1-yloxy)methyl]; 1,3-Propanediol,2-methyl-2-[(2-propen-1-yloxy)methyl]; 1,3-Propanediol,2,2-bis[(2-propen-1-yloxy)methyl; and 1,3-Propanediol,2-[(2,3-dibromopropoxy)methyl]-2-[(2-propen-1-yloxy)methyl]. Furthercompounds within the scope of formula (1) or formula (2) may be known toa person having ordinary skill in the art, and may be used in thepresent disclosure.

The weight ratio of crosslinked thermoplastic polyurethane elastomer tothe unsaturated diols may generally be from about 100:0.1 to about100:25. In particular embodiments, the weight ratio of crosslinkedthermoplastic polyurethane elastomer to the unsaturated diols may beabout 100:10. Furthermore, the NCO index of the reactants making up thecrosslinked thermoplastic polyurethane elastomer may be from about 0.9to about 1.3. As is generally known, the NCO index is the molar ratio ofisocyanate functional groups to active hydrogen containing groups. Inparticular embodiments, the NCO index may be about 1.0.

Optionally, the crosslinked thermoplastic polyurethane elastomer mayinclude further components such as fillers and/or additives. Fillers andadditives may be used based on any of a variety of desiredcharacteristics, such as enhancement of physical properties, UV lightresistance, and other properties. For example, to improve UV lightresistance, the crosslinked thermoplastic polyurethane elastomer mayinclude at least one light stabilizer. Light stabilizers may includehindered amines, UV stabilizers, or a mixture thereof.

Inorganic or organic fillers can be also added to the crosslinkedthermoplastic polyurethane elastomer. Suitable inorganic fillers mayinclude silicate minerals, metal oxides, metal salts, clays, metalsilicates, glass fibers, natural fibrous minerals, synthetic fibrousminerals or a mixture thereof. Suitable organic fillers may includecarbon black, fullerene and/or carbon nanotubes, melamine colophony,cellulose fibers, polyamide fibers, polyacrylonitrile fibers,polyurethane fibers, polyester fibers based on aromatic and/aliphaticdicarboxylic acid esters, carbon fibers or a mixture thereof. Theinorganic and organic fillers may be used individually or as a mixturethereof. The total amount of the filler may be from about 0.5 to about30 percent by weight of the polyurethane components.

Flame retardants may also be used to improve the flame resistance of thecrosslinked thermoplastic polyurethane elastomer. Suitable flameretardants may include organic phosphates, metal phosphates, metalpolyphosphates, metal oxides (such as aluminum oxide hydrate, antimonytrioxide, arsenic oxide), metal salts (such as calcium sulfate,expandable graphite), and cyanuric acid derivatives (such as melaminecyanurate). These flame retardants may be used individually or as amixture thereof, and the total amount of the flame retardant may be fromabout 10 to about 35 percent by weight of the polyurethane components.

To improve toughness and compression rebound, the crosslinkedthermoplastic polyurethane elastomer may include at least onedispersant, such as a monomer or oligomer comprising unsaturated bonds.Examples of suitable monomers include styrene, acrylic esters; suitableoligomers include di- and tri-acrylates/methacrylates, esteracrylates/methacrylates, urethane or urea acrylates/methacrylates.

If the outermost layer of a golf ball comprises the crosslinkedthermoplastic polyurethane elastomer, then the crosslinked thermoplasticpolyurethane elastomer may include at least one white pigment to aid inbetter visibility. The white pigment may be selected from the groupconsisting of titanium dioxide, zinc oxide or a mixture thereof.

The crosslinked thermoplastic polyurethane elastomer may generally beformed by a single-screw, twin-screw, or a batch method in order to mixand react all of the ingredients described above. The products of thereaction process may be in the form of pellets or ground chips.

If a single-screw or twin-screw process is used, the dwell times of themolten reaction mixture in the screw extruder may generally be in therange of from about 0.3 to about 10 minutes, and in some embodiments maybe from about 0.4 to about 4 minutes. The temperature of the screwhousing may be in the range of about 70 degrees Celsius to 280 degreesCelsius. The melt leaving the extruder may be chilled and broken downinto small pieces using any method for the following injection orextrusion applications.

If a batch method is used to form the crosslinked thermoplasticpolyurethane elastomer, all the components are molten and mixed togetherwith a high agitated stir at a temperature in the range of about 70degrees Celsius to 120 degrees Celsius for about 1 to about 3 minutes.Subsequently, the mixture is subjected to a post curing process at atemperature in the range of about 70 degrees Celsius to 150 degreesCelsius for about 5 to about 18 hours. The products made by this batchmethod may be comminuted into chips for an injection or extrusionapplication.

FIG. 2 shows a golf ball 200 in accordance with a second embodiment ofthe present disclosure. Golf ball 200 includes a core 230, an innercover layer 220 substantially surrounding core 230, and an outer coverlayer 210 substantially surrounding inner cover layer 220. In someembodiments, both inner cover layer 220 and outer cover layer 210 maycomprise the crosslinked thermoplastic polyurethane elastomer describedherein. In other embodiments, either inner cover layer 220 or outercover layer 210 comprises the crosslinked thermoplastic polyurethaneelastomer described herein. In still other embodiments, outer coverlayer 210 in particular comprises the crosslinked thermoplasticpolyurethane elastomer described herein.

FIG. 3 shows a golf ball 300 in accordance with a third embodiment ofthe present disclosure. Golf ball 300 includes an inner core layer 330,an outer core layer 320 substantially surrounding inner core layer 330,and a cover layer 310 substantially surrounding outer core layer 320. Insome embodiments, cover layer 310 may comprise the crosslinkedthermoplastic polyurethane elastomer described herein.

FIG. 4 shows a golf ball 400 in accordance with a fourth embodiment ofthe present disclosure. Golf ball 400 includes an inner core layer 440,an outer core layer 430 substantially surrounding inner core layer 440,an inner cover layer 420 substantially surrounding outer core layer 430,and an outer cover layer 410 substantially surrounding inner cover layer420. In some embodiments, both inner cover layer 420 and outer coverlayer 410 comprise the crosslinked thermoplastic polyurethane elastomerdescribed herein. In other embodiments, either inner cover layer 420 orouter cover layer 410 may include the crosslinked thermoplasticpolyurethane elastomer described herein. In specific embodiments, outercover layer 410 comprises the crosslinked thermoplastic polyurethaneelastomer described herein.

In any embodiment in which the cover or outer cover layer (i.e. cover110, cover 310, outer cover layer 210, or outer cover layer 410)comprises the crosslinked thermoplastic polyurethane described herein,the cover or outer cover layer may also have certain advantageousphysical properties. For example, a cover or outer cover layer may havedesired hardness value. Specifically, a cover or outer cover layer mayhave a Shore D hardness of from about 40 to about 65, or from about 45to about 60, on the golf ball.

In some embodiments, a cover or outer cover layer comprised of thecrosslinked thermoplastic polyurethane may also have a desired flexuralmodulus value. Values of the flexural modulus are determined accordingto ASTM D790, for example by ASTM D790-10B. In accordance with ASTMD790, the value of the flexural modulus is measured on the slab ofmaterial. The value of the flexural modulus of the cover or outer coverlayer may be from about 200 psi to about 10,000 psi. In someembodiments, the flexural modulus may have a value from about 200 psi toabout 7,000 psi, or from about 200 psi to about 5,000 psi, or from about200 psi to about 4,000 psi, or from about 300 psi to about 5,000 psi, orfrom about 400 psi to about 2,000 psi. In yet other embodiments, theflexural modulus may have a value of from about 200 psi to about 1,000psi. Finally, the flexural modulus may have a value of about 500 psi insome embodiments.

The construction of the golf ball according to the present disclosure isnot limited to the aforementioned embodiments. A golf ball in accordancewith this disclosure may generally take any construction, such as aregulation or non-regulation construction. Regulation golf balls aregolf balls which meet the Rules of Golf as approved by the United StatesGolf Association (USGA).

The crosslinked thermoplastic polyurethane elastomer described variouslyabove may be used to make golf balls by injection molding or compressionmolding. Injection molding may be used in particular embodiments inorder to achieve increased productivity. Generally, the free radicalinitiator may be added to the polymer mixture at any of several stagesduring manufacturing. For example, the radical initiator may be addedduring extrusion of the polymer mixture, or during compression molding.Similarly, the free radical initiator may be activated so as to formcrosslinks during any of several stages of manufacturing. For example,the free radical initiator may be activated by heating during anextrusion process.

For any ball layer(s) other than the layer(s) comprising the crosslinkedthermoplastic polyurethane elastomer, suitable materials may generallybe selected from any of the various materials known to be used in golfball manufacturing. Generally, these other layers may be constructed asdescribed below.

First, in golf balls having an inner core and an outer core, such as areshown in FIGS. 3 and 4, the inner and outer cores may be constructed asmay be generally known in the art of three-piece and four-piece golfball, or as described below.

In certain embodiments, an inner core (such as inner core 330 or innercore 440) may have certain physical properties. For example, an innercore may have a COR value from 0.785 to 0.9, or from 0.795 to 0.89, orfrom 0.8 to 0.88. An inner core may have a first coefficient ofrestitution, where golf ball 200 has a second coefficient ofrestitution, and the first coefficient of restitution is higher than thesecond coefficient of restitution by at least 0.01. The golf ball of thepresent invention may have a coefficient of restitution of at least0.775.

An inner core layer may be made from a highly neutralized acid polymercomposition. Suitable highly neutralized acid polymer compositions mayinclude HPF resins such as HPF1000, HPF2000, HPF AD1027, HPF AD1035, HPFAD1040 and a mixture thereof, all produced by E. I. Dupont de Nemoursand Company. Suitable highly neutralized acid polymer compositions foruse in forming an inner core may comprise a highly neutralized acidpolymer composition and optionally additives, fillers, and/or melt flowmodifiers. For example, the acid polymer may be neutralized to 70% orhigher, including up to 100%, with a suitable cation source, such asmagnesium, sodium, zinc, or potassium.

Suitable additives and fillers include, for example, blowing and foamingagents, optical brighteners, coloring agents, fluorescent agents,whitening agents, UV absorbers, light stabilizers, defoaming agents,processing aids, mica, talc, nanofillers, antioxidants, stabilizers,softening agents, fragrance components, plasticizers, impact modifiers,acid copolymer wax, surfactants; inorganic fillers, such as zinc oxide,titanium dioxide, tin oxide, calcium oxide, magnesium oxide, bariumsulfate, zinc sulfate, calcium carbonate, zinc carbonate, bariumcarbonate, mica, talc, clay, silica, lead silicate, and the like; highspecific gravity metal powder fillers, such as tungsten powder,molybdenum powder, and the like; regrind, i.e., inner core material thatis ground and recycled; and nano-fillers. Suitable melt flow modifiersinclude, for example, fatty acids and salts thereof, polyamides,polyesters, polyacrylates, polyurethanes, polyethers, polyureas,polyhydric alcohols, and combinations thereof.

The inner core may be made by a fabrication method such as hot-pressmolding or injection molding. A diameter of inner core may be in a rangeof about 19 millimeters to about 32 millimeters, or in a range of about21 millimeters to about 30 millimeters, or in a range of about 24millimeters to about 28 millimeters. Inner core may have a surface ShoreD hardness of 40 to 60.

An outer core layer (such as outer core layer 320 or outer core layer430) may comprise material selected from the following groups: (1)thermoplastic materials selected from the group consisting of ionomerresin, highly neutralized acid polymer composition, polyamide resin,polyester resin, polyurethane resin and a mixture thereof; or (2)thermoset materials selected from the group consisting of polyurethaneelastomer, polyamide elastomer, polyurea elastomer, diene-containingpolymer (such as polybutadiene), crosslinked metallocene catalyzedpolyolefin, silicone, and a mixture thereof.

An outer core layer made from thermoset materials may be made bycrosslinking a polybutadiene rubber composition. When other rubber isused in combination with a polybutadiene, it is typical thatpolybutadiene is included as a principal component. Specifically, aproportion of polybutadiene in the entire base rubber is preferablyequal to or greater than 50% by weight, and particularly preferablyequal to or greater than 80% by weight. A polybutadiene having aproportion of cis-1,4 bonds of equal to or greater than 60 mol %, andfurther, equal to or greater than 80 mol % is typical. In someembodiments, cis-1,4-polybutadiene may be used as the base rubber andmixed with other ingredients. In some embodiments, the amount ofcis-1,4-polybutadiene may be at least 50 parts by weight, based on 100parts by weight of the rubber compound.

Various additives may be added to the base rubber to form a compound.The additives may include a cross-linking agent and a filler. In someembodiments, the cross-linking agent may be zinc diacrylate, magnesiumacrylate, zinc methacrylate, or magnesium methacrylate. In someembodiments, zinc diacrylate may provide advantageous resilienceproperties. The filler may be used to increase the specific gravity ofthe material. The filler may include zinc oxide, barium sulfate, calciumcarbonate, or magnesium carbonate. In some embodiments, zinc oxide maybe selected for its advantageous properties. Metal powder, such astungsten, may alternatively be used as a filler to achieve a desiredspecific gravity. In some embodiments, the density of an outer corelayer may be from about 1.05 g/mm³ to about 1.25 g/mm³. Finally, anouter core layer may have a surface Shore D hardness of from 45 to 65 onthe golf ball.

In some embodiments, a polybutadiene synthesized using a rare earthelement catalyst may be used. Excellent resilience performance of a golfball may be achieved by using this polybutadiene. Examples of rare earthelement catalysts include lanthanum series rare earth element compounds.Other catalysts may include an organoaluminum compound, and alumoxaneand halogen containing compounds. A lanthanum series rare earth elementcompound is typical. Polybutadiene obtained by using lanthanum seriesrare earth-based catalysts usually employ a combination of lanthanumseries rare earth (atomic number of 57 to 71) compounds, butparticularly typical is a neodymium compound.

An outer core layer is preferably made by hot-press molding. Suitablevulcanization conditions include, a vulcanization temperature of between130 degrees Celsius and 190 degrees Celsius, and a vulcanization time ofbetween 5 and 20 minutes. To obtain the desired rubber crosslinked bodyfor use as the core in the present invention, the vulcanizingtemperature is preferably at least 140 degrees Celsius.

When an outer core layer in accordance with this disclosure is producedby vulcanizing and curing the rubber composition in the above-describedway, advantageous use may be made of a method in which the vulcanizationstep is divided into two stages: first, the outer core layer material isplaced in an outer core layer-forming mold and subjected to initialvulcanization so as to produce a pair of semi-vulcanized hemisphericalcups, following which a prefabricated inner core layer is placed in oneof the hemispherical cups and is covered by the other hemispherical cup,in which state complete vulcanization is carried out.

The surface of an inner core layer placed in the hemispherical cups maybe roughened before the placement to increase adhesion between an innercore layer and an outer core layer. In some embodiments, inner corelayer surface may be pre-coated with an adhesive or pre-treated withchemical(s) before placing inner core layer in the hemispherical cups toenhance the durability of the golf ball and enable a high rebound.

Finally, an inner cover layer (such as inner cover layer 220 shown inFIG. 2, or inner cover layer 420 shown in FIG. 4) in accordance withthis disclosure may comprise a thermoplastic material. The thermoplasticmaterial of an inner cover layer may comprise at least one of an ionomerresin, a highly neutralized acid polymer composition, a polyamide resin,a polyurethane resin, a polyester resin, and a combination thereof. Insome embodiments, an inner cover layer may comprise the same crosslinkedthermoplastic polyurethane as an outer cover layer (discussed above). Insome embodiments, an inner cover layer comprises an uncrosslinkedthermoplastic polyurethane different from an outer cover layer, while insome embodiments, inner cover layer comprises an entirely different typematerial from outer cover layer.

An inner cover layer may have a thickness of less than 2 millimeters. Insome embodiments, inner cover layer may have a thickness of less than1.5 millimeters. In some embodiments, inner cover layer has a thicknessof less than 1 millimeter. Although inner cover layer may be relativelythin compared the rest of the layers of golf ball 200 or 400, the innercover layer may have the highest Shore D hardness among all layers. Insome embodiments, inner cover layer has a Shore D hardness of at least60 as measured on the curved surface. In some embodiments, inner coverlayer has a Shore D hardness of at least 65 as measured on the curvedsurface. In some embodiments, the density of inner cover layer may befrom about 1.05 g/mm³ to about 1.5 g/mm³ to create a greater moment ofinertia.

After a cover layer of a golf ball or an outer cover layer of a golfball has been molded, the golf ball may undergo various conventionalfinishing processes such as buffing, stamping and painting. The finishedgolf ball may have a compression deformation of 2 to 4 millimeters undera load of 10 to 130 kilograms.

EXAMPLES

Two golf balls in accordance with the present disclosure were fabricatedas described below, and their scuff resistance was compared to severalcomparative examples.

For each golf ball, the core was made from a material selected fromTable 1, and the cover layer was made from a material selected fromTable 2. The amount of the materials listed in Tables 1 and 2 is shownin parts by weight (pbw) or percentages by weight.

TABLE 1 Core Materials Rubber compound: A B TAIPOL ™ BR0150* 100 100Zinc diacrylate 28 25 Zinc oxide 5 5 Barium sulfate 16 18 Peroxide 1 1

TAIPOL™ BRO150 is the trade name of a rubber produced by TaiwanSynthetic Rubber Corp.

TABLE 2 Cover Materials C D E F G H I PTMEG (pbw) 100   100   100 100 BG(pbw) 15   15   15 15 TMPME  10%  10% 0 10% (weight % to totalcomponents) DCP 0.2% 0.5% 0 0 (weight % to total components) MDI (pbw)87.8 87.8 55.0 87.8 (NCO index)  1.01  1.01 1.01 1.01 Texin ® 245 100Elastollan ® 100 1195A Surlyn ® 8940 50 Surlyn ® 9910 50

“PTMEG” is polytetramethylene ether glycol, having a number averagemolecular weight of 2,000, and is commercially available from Invista,under the trade name of Terathane® 2000. “BG” is 1,4-butanediol,commercially available from BASF and other suppliers. “TMPME” istrimethylolpropane monoallylether, commercially available from PerstorpSpecialty Chemicals AB. “DCP” is dicumyl peroxide, commerciallyavailable from LaPorte Chemicals Ltd. Finally, “MDI” is diphenylmethanediisocyanate, commercially available from Huntsman, under the trade nameof Suprasec® 1100.

Cover materials C, D, E and F were formed by mixing PTMEG, BG, TMPME,DCP and MDI in the proportions shown. Specifically, these materials wereprepared by mixing the components in a high agitated stir for 1 minute,starting at a temperature of about 70 degrees Celsius, followed by a10-hour post curing process at a temperature of about 100 degreesCelsius. The post cured polyurethane elastomers are ground into smallchips.

Cover materials G, H and I are conventional golf ball cover materials.Texin® 245 is trade name of thermoplastic polyurethane resin by BayerMaterialScience AG. Elastollan® 1195A is trade name of thermoplasticpolyurethane resin by BASF. Surlyn® 8940 and Surlyn® 9910 are tradenames of ionomeric resin by E. I. DuPont de Nemours and Company.

From the above core materials and cover materials, seven golf balls weremanufactured as shown in Table 3. Generally, the golf balls weremanufactured using conventional injection molding processes known in theart of golf ball manufacturing.

In each case, the core had a diameter of 39.3 millimeters, the totalgolf ball diameter was 42.7 millimeters, and the golf ball's totalweight was 45.4 grams.

TABLE 3 Golf Ball Scuff Resistance Examples Comparative examples 1 2 3 45 6 7 Core—Rubber A A A A A A B Cover Resin C D E F G H I Hardness, 5353 53 53 53 53 69 Shore D Flexural 500 500 500 500 10,000 9,500 49,300Modulus Scuff resistance Rating 2 1 3 4 3 3 4

Identical golf ball precursors comprising 3 layers were covered with theresins numbered “8” through “11” as described in Table 4:

TABLE 4 Additional Scuff Resistance Resin 8 9 10 11 Cross-linked TPU 100Texin-245 100 50 Texin-255 50 100 Material Shore D (on the plaque) 38 4550 55 Flexural Modulus, psi 500 10,000 N/A 20,000

The scuff resistance was evaluated (in accordance with the protocol setforth below. The balls were ranked, from best to worst scuff resistance,as follows: 8>9>10>11.

The scuff resistance test was conducted in the following manner: a NikeVictory Red forged standard sand wedge (loft: 54°; bounce: 12°; shaft:True Temper Dynamic Gold shaft; flex: S) is fixed to a swing robotmanufactured by Miyamae Co., Ltd. and then swung at the head speed ofabout 32 m/s. The club face was oriented for a square hit. Theforward/backward tee position was adjusted so that the tee was fourinches behind the point in the downswing where the club was vertical.The height of the tee and the toe-heel position of the club relative tothe tee were adjusted in order that the center of the impact mark wasabout ¾ of an inch above the sole and was centered toe to heel acrossthe face. Three samples of each ball were tested. Each ball was hitthree times.

Other methods may also be used to determine the scuff resistance, suchas the methods described in the commonly assigned copending applicationtitled “Golf Ball Wear Indicator”, U.S. Patent and Trademark Office Ser.No. 12/691,282, filed Jan. 21, 2010 in the name of Brad Tutmark.

After the above described scuff resistance testing, each golf ball coverwas visually observed and rated according to the following scale: a golfball cover was rated “1” when little or no damage was visible, onlygroove markings or dents; a golf ball cover was rated “2” when smallcuts and/or ripples in the cover were apparent; a golf ball cover wasrated “3” when moderate amounts of cover material were lifted from theball's surface, but the cover material was still attached to the ball;and finally a golf ball cover was rated “4” when cover material wasremoved or barely attached to the golf ball.

Unless otherwise noted, Shore D hardness values of the core and coverlayer were measured on the spherical surface of the layer to be measuredby using a Shore D hardness tester.

As shown in Table 3, golf ball examples 1 and 2 made from compositionsincluding a crosslinked thermoplastic polyurethane elastomer havingcrosslinks located in the hard segments, where the crosslinks are thereaction product of unsaturated bonds located in the hard segmentscatalyzed by a free radical initiator, provide superior scuff resistanceas compared to cover compositions that do not include crosslinks.

While various embodiments of the invention have been described, thedescription is intended to be exemplary, rather than limiting and itwill be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof the invention. Accordingly, the invention is not to be restrictedexcept in light of the attached claims and their equivalents. Also,various modifications and changes may be made within the scope of theattached claims.

1. A golf ball comprising: a core, and a cover layer substantiallysurrounding the core; wherein the cover layer comprises a crosslinkedthermoplastic polyurethane elastomer; the crosslinked thermoplasticpolyurethane elastomer including hard segments and soft segments, thecrosslinked thermoplastic polyurethane elastomer including crosslinkslocated in the hard segments, the crosslinks being the reaction productof unsaturated bonds located in the hard segments catalyzed by a freeradical initiator; and wherein the cover layer has a flexural modulus offrom about 200 psi to about 10,000 psi.
 2. The golf ball of claim 1,wherein the cover layer further comprises an inner cover layersubstantially surrounding the core and an outer cover layersubstantially surrounding the inner cover layer; and the outer coverlayer comprises the crosslinked thermoplastic polyurethane elastomerhaving crosslinks located in the hard segments.
 3. The golf ball ofclaim 2, wherein the outer cover layer has a Shore D hardness of fromabout 40 to about 65 on the golf ball, and the outer cover layer has theflexural modulus of from about 200 psi to about 10,000 psi.
 4. The golfball of claim 1, wherein the cover layer further comprises an innercover layer substantially surrounding the core and an outer cover layersubstantially surrounding the inner cover layer; and the inner coverlayer comprises the crosslinked thermoplastic polyurethane elastomerhaving crosslinks located in the hard segments.
 5. The golf ball ofclaim 1, wherein the crosslinked thermoplastic polyurethane elastomer isthe reaction product of a reaction mixture including an unsaturated diolhaving a pendant side chain that includes a terminal unsaturated bond asa chain extender.
 6. The golf ball of claim 1, wherein the crosslinkedthermoplastic polyurethane elastomer is the reaction product of anunsaturated diol of formula (1):

in which R¹ may be any substituted or unsubstituted alkyl, substitutedor unsubstituted aryl, substituted or unsubstituted alkyl-aryl group,substituted or unsubstituted ether group, substituted or unsubstitutedester group, any combination of the above groups, or H, and mayoptionally include an unsaturated bond in any main chain or side chainof any group; R² may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups, or acontinuation of the single bond, and R² includes an allyl group; and xand y are integers independently having any value from 1 to
 10. 7. Thegolf ball of claim 1, wherein the crosslinked thermoplastic polyurethaneelastomer is the reaction product of an unsaturated diol of formula (2):

in which R is a substituted or unsubstituted alkyl group, and x and yare integers independently having any value from 1 to
 4. 8. The golfball of claim 1, wherein the crosslinked thermoplastic polyurethaneelastomer is the reaction product of trimethylolpropane monoallyletheras a chain extender.
 9. The golf ball of claim 1, wherein the coverlayer has a Shore D hardness of between about 40 and about 65 on thegolf ball.
 10. The golf ball of claim 9, wherein the cover layer has aShore D hardness of between about 45 and about 60 on the golf ball. 11.The golf ball of claim 1, wherein the cover layer has a flexural modulusof from about 200 psi to about 7,000 psi.
 12. The golf ball of claim 11,wherein the cover layer has a flexural modulus of from about 200 psi toabout 1,000 psi.
 13. The golf ball of claim 1, wherein the crosslinkedthermoplastic polyurethane elastomer is the reaction product formed fromreacting a reaction mixture of: (a) an organic isocyanate; (b) anunsaturated diol first chain extender; (c) a long chain polyol having amolecular weight of between about 500 and about 4,000; and (d) asufficient amount of free radical initiator, so as to be capable ofgenerating free radicals that induce crosslinking structures in the hardsegments by free radical initiation.
 14. The golf ball of claim 13,wherein the free radical initiator is selected from the group consistingof peroxides, sulfurs, sulfides, and mixtures thereof.
 15. The golf ballof claim 13, wherein the reaction mixture further includes a secondchain extender, the second chain extender having at least two reactionsites with isocyanates and having a molecular weight of less than about450.
 16. A golf ball comprising: a core, and a cover layer substantiallysurrounding the core; wherein the cover layer comprises a crosslinkedthermoplastic polyurethane elastomer; the crosslinked thermoplasticpolyurethane elastomer including hard segments and soft segments, thecrosslinked thermoplastic polyurethane elastomer including crosslinkslocated in the hard segments, the crosslinks being the reaction productof unsaturated bonds located in the hard segments catalyzed by a freeradical initiator; and wherein the crosslinked thermoplasticpolyurethane elastomer is the reaction product of an unsaturated diol offormula (1):

in which R¹ may be any suitable substituted or unsubstituted alkyl,substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups, or H,and may optionally include an unsaturated bond in any main chain or sidechain of any group; R² may be any suitable substituted or unsubstitutedalkyl, substituted or unsubstituted aryl, substituted or unsubstitutedalkyl-aryl group, substituted or unsubstituted ether group, substitutedor unsubstituted ester group, any combination of the above groups, or acontinuation of the single bond, and R² includes an allyl group; and xand y are integers independently having any value from 1 to
 10. 17. Thegolf ball of claim 16, wherein the cover layer has a flexural modulus offrom about 200 psi and about 10,000 psi.
 18. The golf ball of claim 16,wherein the cover layer has a Shore D hardness of from about 40 to about65 on the golf ball.
 19. A golf ball comprising: an inner core layer, anouter core layer substantially surrounding the inner core layer, aninner cover layer substantially surrounding the outer core layer, and anouter cover layer substantially surrounding the inner cover layer;wherein the outer cover layer comprises a crosslinked thermoplasticpolyurethane elastomer having crosslinks located in hard segments, thecrosslinks being the reaction product of unsaturated bonds located inthe hard segments catalyzed by a free radical initiator; and the golfball satisfies the following requirements: (1) the outer cover layer hasa Shore D hardness from about 40 to about 65 on the golf ball; and (2)the outer cover layer has a flexural modulus of from about 200 psi toabout 10,000 psi.
 20. The golf ball of claim 19, wherein the crosslinkedthermoplastic polyurethane elastomer is the reaction product formed fromreacting a reaction mixture of: (a) trimethylolpropane monoallylether asa first chain extender; (b) a second chain extender, having at least tworeaction sites with isocyantes and having a molecular weight of lessthan about 450; (c) a long chain polyol having a molecular weight ofbetween about 500 and about 4,000; and (d) a sufficient amount of freeradical initiator, so as to be capable of generating free radicals thatinduce crosslinking structures in the hard segments by free radicalinitiation.